Since the beginning of the art of installing oil and gas wells underwater, installation of the flowlines necessary to carry produced fluid away from the wellhead or to carry produced fluid to or processed fluid from, e.g., a manifold has presented a difficult problem. When wells were installed in shallow water, it was possible to practice methods and use connectors and other apparatus which could be directly manipulated by divers. As locations for wells and other installations began to present water depths beyond reasonable diver assistance capabilities, a number of approaches were adopted which provided for making up the connection between the flowline and, e.g., a wellhead by completely remote operations, carried out from a platform, a semi-submersible, a drilling vessel or other operational base at the surface of the body of water, without diver assistance. Most such approaches depend upon laying the flowline from a barge, one end of the line first being lowered to the bottom adjacent the installation to which connection is to be made, the barge then moving off location to lay the flowline on the bottom of the body of water. In some cases, the flowline end to be connected has been maintained in a vertically downward orientation while being lowered and has been stabbed into a connector part carried by the wellhead or other apparatus, orientation of the flowline relative to the connector part being maintained by conventional guide means. In other cases, a receiving funnel is provided at the installation where the flowline is to be connected and the end of the flowline is hauled into the funnel by a wireline, termination of the hauling operation serving to secure a male or female connector part carried by the flowline end. Such receiving funnels have in some cases been horizontally disposed, but greater promise has been offered by such approaches when the funnel is in the form of a J-tube with the end of the funnel which is to be entered by the flowline being approximately horizontal and the opposite end being upright. Though these and other methods and apparatus provided by the prior art have achieved acceptance in the field, the task of installing and connecting flowlines presents some problems which have not heretofore been solved completely, and there has been a continuing need for improvement.
Though remote installations under water inherently present severe problems, the problems of installing and connecting flowlines are made more difficult by the nature of the flowlines themselves. Since the flowline in most installations is in the form of a metal pipe of significant diameter, any bend in the pipe is necessarily of large radius. Thus, for a flowline 2 or 3 inches in diameter, the radius for any turn of the free line is on the order of 15-25 feet and, for a 6 inch flowline, the radius of curvature is typically 35-45 feet. Further, since the flowline is not only relatively stiff but also relatively heavy, the forces involved in moving the flowline are relatively large. Thus, to pull the end portion of a flowline through a J-tube type of receiving funnel requires a pulling force on the order of 7,500 pounds for a small diameter flowline. The effect of such pulling forces is worsened by the fact that when the flowline end is hauled toward the wellhead or other installation, the lowered end of the flowline is not likely to be aligned with the received tube. In many cases, with the end of the flowline attached to one end of a wireline and lowered from a barge, the initial position of the wireline-attached flowline end may be almost anywhere along a 360.degree. circle around the wellhead or other installation when the installation is at a great depth. Workers in the prior art have recognized such problems and the art has developed in a direction tending to solve them, as disclosed, for example, in the following U.S. patents:
U.S. Pat. No. 3,378,066, Otteman et al PA1 U.S. Pat. No. 3,298,092, Dozier et al PA1 U.S. Pat. No. 4,175,620 Nolan et al
However, no method and apparatus provided by the prior art has proved fully satisfactory, particularly for subsea installations at great depths.